Pregabalin (I, PGB), chemical name (S)-3-(aminomethyl)-5-methylhexanoic acid (I), is a 3-isobutyl substituted γ-aminobutanoic acid (Angew. Chem. Int. Ed. 2008, 47: 3500-3504). PGB is very effective in treating epilepsy, diabetic neuropathy pain, and post-herpetic neuralgia pain. It requires lower dosages and less frequent administration, has fewer side effects, lasts longer, and is well tolerated. PGB has become a blockbuster in global pharmaceutical markets.
(S)-3-Cyano-5-methylhexanoic acid (II) is a key chiral intermediate that can be converted to PGB through hydrogenation. Pfizer, Inc. has developed a second-generation, enzymatic process for PGB, where 2-carboxyethyl-3-cyano-5-methylhexanoic acid ethyl ester diethyl 2-(1-cyano-3-methylbutyl)malonate was resolved through Lipolase® catalysis, decarboxylated, and hydrolyzed under basic condition to afford II (Org. Process Res. Dev. 2008, 12: 392-398). This process requires decarboxylation and two hydrolysis steps, leading to low atom economy.

Nitrilase (EC 3.5.5.1) is an enzyme that can catalyze the hydrolysis of nitriles to ammonia and the corresponding carboxylic acid. Nitrilase has very strict regio- and stereo-selectivity and shows high potential in the manufacture of highly valuable active pharmaceutical ingredients. Pfizer's Xie reported that Arabidopsis thaliana nitrilase At-Nit1 could regio- and stereo-selectively convert racemic 2-isobutylsuccinonitrile (ISBN) into II (J. Mol. Catal. B: Enzym. 2006, 41:75-80). This process enjoys a very high atom economy. However, nitrilase At-Nit1 has low activity and only provides II with 17.5% yield when the substrate concentration was 150 mM (WO2005100580). Another enzyme NIT-102 could only provide II at 31.3% when the substrate was treated for 24 hr at 400 mM (WO2005100580). This method is difficult to industrialize because of the long reaction time and low substrate concentration. Thus, it is very necessary to find nitrilases with industrial potential for the manufacturing of II.